Database Programming with PL/SQL - Dixie State University · • Create PL/SQL code to process the rows of an active set using record types in cursors • Retrieve information about

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Database Programming with PL/SQL 5-2 Using Explicit Cursor Attributes

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. PLSQL S5L2 Using Explicit Cursor Attributes

Objectives

This lesson covers the following objectives: • Define a record structure using the %ROWTYPE attribute

• Create PL/SQL code to process the rows of an active set using record types in cursors

• Retrieve information about the state of an explicit cursor using cursor attributes

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Purpose

• One of the reasons to use explicit cursors is that they give you greater programmatic control when handling your data.

• This lesson discusses techniques for using explicit cursors more effectively.

• Cursor records enable you to declare a single variable for all the selected columns in a cursor.

• Cursor attributes enable you to retrieve information about the state of your explicit cursor.

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Cursors and Records

• The cursor in this example is based on a SELECT statement that retrieves only two columns of each table row.

• What if it retrieved six columns .. or seven, or eight, or twenty? DECLARE v_emp_id employees.employee_id%TYPE; v_last_name employees.last_name%TYPE; CURSOR cur_emps IS SELECT employee_id, last_name FROM employees WHERE department_id = 30; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_id, v_last_name; ...

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Cursors and Records

• This cursor retrieves whole rows of EMPLOYEES. • Imagine the list of declarations with all columns listed. DECLARE v_emp_id employees.employee_id%TYPE; v_first_name employees.first_name%TYPE; v_last_name employees.last_name%TYPE; v_email employees.email%TYPE; v_phone_number employees.phone_number%TYPE; ... v_department_id employees.department_id%TYPE; CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_id, v_first_name, v_last_name ... v_department_id; ...

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Cursors and Records

• Compare the following snippets of code. • What differences do you see? DECLARE v_emp_id ...; v_first_name ...; ... v_department_id ...: CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_id, v_first_name, ... v_department_id; ...

DECLARE CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; v_emp_record cur_emps%ROWTYPE; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_record; ...

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Cursors and Records

• The code on the right uses %ROWTYPE to declare a record structure based on the cursor.

• A record is a composite data type in PL/SQL. DECLARE v_emp_id ...; v_first_name ...; ... v_department_id ...: CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_id, v_first_name, ... v_department_id; ...

DECLARE CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; v_emp_record cur_emps%ROWTYPE; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_record; ...

Variables Records

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• A record is a composite data type, consisting of a number of fields each with their own name and data type.

• You reference each field by dot-prefixing its field-name with the record-name.

• %ROWTYPE declares a record with the same fields as the cursor on which it is based.

Structure of a PL/SQL Record

Field1 (data type) Field2 (data type) Field3 (data type) …

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Structure of a PL/SQL Record

DECLARE CURSOR cur_emps IS SELECT employee_id, last_name, salary FROM employees WHERE department_id = 30; v_emp_record cur_emps%ROWTYPE; ...

v_emp_record.employee_id v_emp_record.last_name v_emp_record.salary …

100 King 24000

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Cursors and %ROWTYPE

%ROWTYPE is convenient for processing the rows of the active set because you can simply fetch into the record.

DECLARE CURSOR cur_emps IS SELECT * FROM employees WHERE department_id = 30; v_emp_record cur_emps%ROWTYPE; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_record; EXIT WHEN cur_emps%NOTFOUND; DBMS_OUTPUT.PUT_LINE(v_emp_record.employee_id || ' - ' || v_emp_record.last_name); END LOOP; CLOSE cur_emps; END;

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How many fields does v_emp_dept_record contain, and what are they?

Cursors and %ROWTYPE: Another Example

DECLARE CURSOR cur_emps_dept IS SELECT first_name, last_name, department_name FROM employees e, departments d WHERE e.department_id = d.department_id; v_emp_dept_record cur_emps_dept%ROWTYPE; BEGIN OPEN cur_emps_dept; LOOP FETCH cur_emps_dept INTO v_emp_dept_record; EXIT WHEN cur_emps_dept%NOTFOUND; DBMS_OUTPUT.PUT_LINE(v_emp_dept_record.first_name || ' – ' || v_emp_dept_record.last_name || ' – ' || v_emp_dept_record.department_name); END LOOP; CLOSE cur_emps_dept; END;

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Explicit Cursor Attributes

• As with implicit cursors, there are several attributes for obtaining status information about an explicit cursor.

• When appended to the cursor variable name, these attributes return useful information about the execution of a cursor manipulation statement.

Attribute Type Description %ISOPEN Boolean Evaluates to TRUE if the cursor is open.

%NOTFOUND Boolean Evaluates to TRUE if the most recent fetch did not return a row.

%FOUND Boolean Evaluates to TRUE if the most recent fetch returned a row; opposite of %NOTFOUND.

%ROWCOUNT Number Evaluates to the total number of rows FETCHed so far.

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%ISOPEN Attribute

• You can fetch rows only when the cursor is open. • Use the %ISOPEN cursor attribute before performing a

fetch to test whether the cursor is open. • %ISOPEN returns the status of the cursor: TRUE if open

and FALSE if not.

• Example: IF NOT cur_emps%ISOPEN THEN OPEN cur_emps; END IF; LOOP FETCH cur_emps...

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%ROWCOUNT and %NOTFOUND Attributes

• Usually the %ROWCOUNT and %NOTFOUND attributes are used in a loop to determine when to exit the loop.

• Use the %ROWCOUNT cursor attribute for the following: – To process an exact number of rows

– To count the number of rows fetched so far in a loop and/or determine when to exit the loop

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%ROWCOUNT and %NOTFOUND Attributes

Use the %NOTFOUND cursor attribute for the following: • To determine whether the query found any rows matching

your criteria • To determine when to exit the loop

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Example of %ROWCOUNT and %NOTFOUND

This example shows how you can use %ROWCOUNT and %NOTFOUND attributes for exit conditions in a loop. DECLARE CURSOR cur_emps IS SELECT employee_id, last_name FROM employees; v_emp_record emp_cursor%ROWTYPE; BEGIN OPEN emp_cursor; LOOP FETCH cur_emps INTO v_emp_record; EXIT WHEN cur_emps%ROWCOUNT > 10 OR cur_emps%NOTFOUND; DBMS_OUTPUT.PUT_LINE(v_emp_record.employee_id || ' ' || v_emp_record.last_name); END LOOP; CLOSE cur_emps; END;

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Explicit Cursor Attributes in SQL Statements

• You cannot use an explicit cursor attribute directly in an SQL statement.

• The following code returns an error: DECLARE CURSOR cur_emps IS SELECT employee_id, salary FROM employees ORDER BY SALARY DESC; v_emp_record cur_emps%ROWTYPE; v_count NUMBER; BEGIN OPEN cur_emps; LOOP FETCH cur_emps INTO v_emp_record; EXIT WHEN cur_emps%NOTFOUND; INSERT INTO top_paid_emps (employee_id, rank, salary) VALUES (v_emp_record.employee_id, cur_emps%ROWCOUNT, v_emp_record.salary); ...

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Terminology

Key terms used in this lesson included: • %ISOPEN • %NOTFOUND

• Record • %ROWCOUNT • %ROWTYPE

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Summary

In this lesson, you should have learned how to: • Define a record structure using the %ROWTYPE attribute

• Create PL/SQL code to process the rows of an active set using record types in cursors

• Retrieve information about the state of an explicit cursor using cursor attributes

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Documents

Database Programming with PL/SQL - Dixie State University · • Create PL/SQL code to process the rows of an active set using record types in cursors • Retrieve information about